This invention relates to the general subject of methods and devices for recovering fluids from subterranean formations, and, in particular, to processes and apparatus for recovering bitumen, heavy crude oil and other hydrocarbons by means of horizontal wells drilled from surface locations.
It is well known that the use of horizontal wells drilled from surface locations has improved the economics and reduced the environmental impact of finding and recovering hydrocarbons and other substances from subterranean formations. A horizontal well is a well that is formed with a section of the well being oriented relatively or approximately in a geometric plane that is parallel to the surface of the earth beneath which such section is located. In particular it is well known that in appropriate applications, a single horizontal well can expose and access as much of the mineral bearing rock in a subterranean formation as several vertical wells. A vertical well is a well which is not comprised in whole or in part of a horizontal section as described above, and includes a deviated or slant hole well formed or drilled from the surface of the earth.
The cost of drilling and completing a single horizontal well into a particular formation, generally exceeds the cost of drilling and completing a vertical well into the same formation. However substantial economies of scale can be achieved where the use of horizontal wells significantly reduces the number of wells required to efficiently produce the hydrocarbons contained in a subterranean reservoir. These savings accrue as a result of reduced capital and operating costs for developing and producing a mineral bearing subterranean formation. For an excellent summary of the art and advantages of producing a subterranean reservoir using horizontal wells, see:
Butler, R. M., xe2x80x9cThe Potential for Horizontal wells for petroleum productionxe2x80x9d, Journal of Canadian Petroleum Technology, May-June 1989, Volume 28, No. 3, pp.39-47;
Deskins, W. G, Reid, T. B. and McDonald, W. J., xe2x80x9cSuccess of Horizontal Well Technology in Heavy Oil Applicationsxe2x80x9d, 6th UNITAR International Conference on Heavy Crude and Tar Sands, Feb. 12-17, 1995, Houston Tex., USA, Volume 1, pp. 495-503; and
Thakur, G. C., xe2x80x9cHorizontal Well Technologyxe2x80x94A Key to Improving Reservesxe2x80x9d, paper delivered at the SPE/CIM 5th Annual One-day Conference on Improvement in Horizontal Well Productivity and Profitability, Calgary, Alberta, Canada, Nov. 21, 1995.
A hydrocarbon bearing subterranean formation is usually developed and produced through wells formed from locations on the surface of the earth overlying such formation. It is well known that the use of horizontal wells can reduce the number of wells required to accomplish such development and production which in turn, can correspondingly reduce the number and areal extent of well sites and access roads required to form and support such wells. As a result the cost and environmental impact of developing and producing a hydrocarbon bearing subterranean formation can be reduced.
It is well known in the art that a subterranean reservoir containing hydrocarbons or other valuable substances which are fluid in nature or may be reduced to or carried in a fluid, can be produced efficiently through a network of horizontal well-bores. A means of exploiting and producing substances contained in a subterranean reservoir through a network of horizontal wells is disclosed in U.S. Pat. No. 4,621,691 to Shuh. However the method taught by Shuh requires that each horizontal well be drilled from a separate well site, and completed, equipped and operated as a separate individual well.
As improvements in technology have facilitated the drilling of horizontal wells of increasing length and at shallower depths, further reductions in the environmental impact and economic cost of developing a subterranean hydrocarbon reservoir have been achieved by drilling multiple horizontal wells from the same well site or drilling xe2x80x9cpadxe2x80x9d (see Sadler, K. W. and Houlihan, R. N. xe2x80x9cAn Energy Resources Conservation board Review of Oil Sands Development in Alberta, 6th UNITAR International Conference on Heavy Crude and Tar Sands, Feb. 12-17, 1995, Houston Tex., USA, Volume 1, p. 95-103, at pp.101 and 102). In these instance the well-bore of each well drilled from the pad is characterized by having its own vertical, build and horizontal sections. The vertical section lies approximately perpendicular to the surface of the earth from which the well is formed. The horizontal section lies approximately parallel to the surface of the earth. The build section is the portion of the well-bore which connects the horizontal section and the vertical section. Although multiple well-bores may be formed from a single well site, frequently each well-bore is completed, equipped and operated as a separate individual well. By completing, it is meant that steps are taken to prevent: (i) the collapse of the well-bore, (ii) the infiltration of substances into the well-bore from formations other the target formation, (iii) the ex-filtration of substances from the well-bore into formations other the target formation, and (iv) the uncontrolled escape of substances from the subterranean formations penetrated by the well-bore. By equipping, it is meant that steps are taken to prepare the well-bore to be used to inject or produce substances, into or from the subterranean formation, as the case may be. This includes the placing of pumps, production or injection tubing and other equipment into the well-bore and the installation and connection of tanks, pumps, surface piping or other equipment at surface on the well site and to the well-bore as the case may be.
To overcome the need to complete and equip each well formed from a pad site, advances in the art discloses the forming of multiple well-bores from a single vertical shaft and the apparatus required to form, operate and maintain such multiple well-bores. This allows more of the reservoir to be accessed from a single well site using a network of multiple horizontal well-bores that share a common vertical section. This further reduces the amount of surface disturbance. The size of the well site required to support multiple horizontal well-bores formed and operated in this fashion, may be smaller than the well site required to form and operate a similar number of horizontal well-bores formed from individual vertical sections. See:
Maurer, W. C., xe2x80x9cRecent Advances in Horizontal Drillingxe2x80x9d, The Journal of Canadian Petroleum Technology, Nov. 1995, Volume 34, No. 9, pp. 25-33.
Brockman, M. and Gann, C., xe2x80x9cMultilateral Completions Prepare to Take Offxe2x80x9d, Petroleum Engineer International, January 1996, pp. 49-50.
Themig, D., xe2x80x9cPlanning And Evaluation Are Crucial To Multilateral Wellsxe2x80x9d, Petroleum Engineer International, January 1996, pp. 53-57.
Collins, D., xe2x80x9cSingle-Size Reduction Offers Workover, Completion Advantagesxe2x80x9d, Petroleum Engineer International, January 1996, pp. 5942.
Von Flatern, R., xe2x80x9cOperators Are Ready For More Sophisticated Multilateral Well Technologyxe2x80x9d, Petroleum Engineer International, January 1996, pp. 6549.
Sperry-sun Drilling Services Brochure xe2x80x9cHorizontal Drilling; Multilateral and Twinned Wellsxe2x80x9d, copyright 1993, Sperry-Sun Drilling Services Inc.
U.S. Pat. No. 4,020,901 to Piso et al
U.S. Pat. No. 4,022,279 to Driver
U.S. Pat. No. 4,160,481 to Turk et al
U.S. Pat. No. 4,257,650 to Allen
U.S. Pat. No. 4,379,592 to Vakhnin et al
U.S. Pat. No. 4,434,849 to Allen
U.S. Pat. No. 4,442,896 to Reale et al
U.S. Pat. No. 4,458,945 to Ayler et al
U.S. Pat. No. 4,463,988 to Bouck et al
U.S. Pat. No. 4,519,463 to Schuh
U.S. Pat. No. 4,595,239 to Ayler et al
U.S. Pat. No. 4,611,855 to Richards
U.S. Pat. No. 4,753,485 to Goddhart
U.S. Pat. No. 4,982,786 to Jennnings Jr.
U.S. Pat. No. 5,115,872 to Brunet et al
U.S. Pat. No. 5,123,488 to Jennings Jr.
U.S. Pat. No. 5,311,936 to McNair et al
U.S. Pat. No. 5,330,007 to Collins et al
U.S. Pat. No. 5,394,950 to Gardes
U.S. Pat. No. 5,425,429 to Thompson
U.S. Pat. No. 5,427,177 to Jordan Jr. et al
U.S. Pat. No. 5,435,392 to Kennedy et al
U.S. Pat. No. 5,458,199 to Collins et al
U.S. Pat. No. 5,458,209 to Hayes et al
U.S. Pat. No. 5,474,131 to Jordan, Jr. et al
U.S. Pat. No. 5,477,293 to Jordan, Jr. et al
U.S. Pat. No. 5,526,880 to Jordan, Jr. et al
U.S. Pat. No. 5,533,573 to Jordan, Jr. et al
However, practice of the methods and apparatus disclosed by the foregoing art is expensive and requires the employment of complicated mechanisms and procedures. The construction of a network of horizontal well-bores according to the foregoing art, requires that all well-bores must communicate by physically intersecting or connecting. By communicate, it is meant that fluids, either gas or liquid, which enter one well-bore in the network, may flow or drain to another well-bore in the network. By intersecting or connecting, it is meant that each well-bore is directly joined or coupled to: (i) at least one other horizontal well-bore to form a continuous bore hole composed of such joined or coupled well-bores, or (ii) a common shared vertical section.
Due to limitations in drilling technology, the area of the reservoir that can be accessed and produced through the practice of current multi-well technology is limited. Also the efficient employment of these technologies to form a network of communicating horizontal wells usually requires that the entire network be constructed before employing the network to produce substances from the target reservoir. In most cases the construction of the network in phases, while physically possible, is usually not economic.
Other technologies disclosed by the art attempt to overcome these limitations by disclosing intersecting well-bores drilled separately from different locations. See:
U.S. Pat. No. 3,386,508 to Bielstein et al
U.S. Pat. No. 3,513,913 to Bruist
U.S. Pat. No. 3,892,270 to Lindquist
U.S. Pat. No. 3,986,557 to Striegler
U.S. Pat. No. 4,007,788 to Striegler
U.S. Pat. No. 4,016,942 to Wallis, Jr. et al
U.S. Pat. No. 4.037,658 to Anderson
U.S. Pat. No. 4,220,203 to Steeman
U.S. Pat. No. 4,368,781 to Anderson
U.S. Pat. No. 4,390,067 to Willman
U.S. Pat. No. 4,442,896 to Reale
U.S. Pat. No. 4,511,000 to Mims
U.S. Pat. No. 4,532,986 o Mims et al
U.S. Pat. No. 5,016,710 to Renard et al
U.S. Pat. No. 5,074,360 to Guinn
U.S. Pat. No. 5,402,851 to Baiton
U.S. Pat. No. 5,450,902 to Mathews
This allows the network of wells to be formed in phases. However this still requires that the well-bores must connect or intersect. In practice, this has proven expensive and difficult to implement. What is required is an alternative method that will allow a large area of a subterranean reservoir to be accessed through and affected by a network of horizontal well-bores without:
(i) using complex and expensive drilling, completion and production equipment and techniques;
(ii) having to intersect or connect each well-bore with the other well-bores in the network;
(iii) having to equip and operate each well-bore separately; and
(iv) having to construct the entire network immediately before being able to utilize any portion of the network.
U.S. Pat. No. 4,522,260 to Wolcott, Jr. teaches the formation of a network of horizontal well-bores and the use of explosives detonated in such well-bores in order to rubblize the solid material comprising the reservoir. Wolcott teaches that the rubblizing of the formation creates improved permeability in the reservoir, thereby allowing fluids to more readily flow or drain from the reservoir into the wells. However, the rendering of a solid or consolidated reservoir matrix into an unconsolidated matrix, would not provide a sufficient enhancement to the ability of liquids to flow through the reservoir. Those skilled in the art will realize that in order for liquids to flow efficiently through a subterranean reservoir, a channel or conduit must exist or be created.
Furthermore, much of the world""s heavy crude oil and bitumen deposits are found in reservoirs comprised of unconsolidated materials, such as oil sands. The instability of the reservoir matrix in these situations makes the application of Wolcott impossible. Those skilled in the art will also realize that the method taught by Wolcott would be difficult to apply to a thin reservoir. For example, in the Wabasca Area of Alberta, Canada, heavy crude oil has been found and produced from reservoirs less than 6 metres in thickness. The detonation of any significant amount of explosive in such a thin reservoir would risk rupturing the impermeable layers of rock which underlie and overlay the reservoir.
The practice of Wolcott in a reservoir comprised of consolidated materials, would result in the collapse of substantial portions of the horizontal sections of the well-bores comprising the network of wells formed according to this method. This is a natural result of transforming the consolidated reservoir matrix into an unconsolidated matrix.
Finally Wolcott does not teach any method of reducing the cost and environmental impact of producing fluids from a reservoir through a network of wells. Wolcott does not prescribe using less than all wells in the network to produce fluids from the reservoir. Wolcott refers to the application of methods known in the art to accomplish such production of fluids.
It is well known in the art, that the use of vertical or horizontal wells to produce fluids from a subterranean formation comprised of unconsolidated material, will frequently result in the production of solid material from the formation with the fluid. In many instances this has been observed to result in the formation of conduits within the formation. It is believed that the formation of such conduits can extend the area of the formation affected by an individual well. By conduit, it is meant that a channel or passage is created within and relatively free of the solid material which comprises the subterranean formation. See:
Smith, G. E., xe2x80x9cFluid Flow in Heavy Oil Reservoirs Under Primary Depletion and Their Apparent Enhanced Permeabilityxe2x80x9d, Presented at the SEG/SIAM/SPE Conference entitled, Mathematical and Computations Methods In Seismic Exploration and Reservoir Modeling, held January 21-24, 1985, in Houston Tex., USA
Smith, G. E., xe2x80x9cSand Production By Gross Formation Failurexe2x80x9d, Presented at the CIM Lloydminster Heavy Oil Seminar, held Nov. 5, 1985, in Lloydminister, Alberta, Canada.
Squires, A., xe2x80x9cInter-well Tracer Results and Gel Blocking Program Clearwater Reservoir, Elk Point, Albertaxe2x80x9d, Presented at the Canadian Heavy Oil Association Tenth Annual Heavy Oil and Oil Sands Technical Symposium, Mar. 9, 1993
The formation of such conduits can greatly extend the area of the reservoir which can be accessed and affected by the wells connected to such conduits. However, conduits formed in the manner described in the foregoing art are unreliable, as the direction, extent and stability of such conduits cannot be controlled or maintained. Furthermore, as disclosed in the foregoing articles, the uncontrollable nature of such naturally formed conduits can be detrimental to the production of hydrocarbons from a reservoir.
It is also well known in the art, that one o the major problems encountered in drilling a horizontal well, is the loss of circulation. This occurs when large volumes of drilling fluid escape into the formation being penetrated by the drill string. When drilling a horizontal well in the vicinity of existing well-bores which are being produced or have been produced, the loss of circulation is common. Frequently the production of fluids from existing offsetting wells must be temporarily suspended while drilling operations of the new well are under way, in order to mitigate the possibility of loss of circulation occurring, or the contamination of offsetting producing wells with drilling fluid.
It is an objective of the apparatus and process described herein to take advantage of both of the foregoing phenomena, by teaching the construction and operation a network of communicating horizontal wells without requiring the employment of complex equipment and processes, and without the need for such wells to intersect. Such a method and apparatus has particular application in the production of heavy viscous fluids such a bitumen and heavy crude oil. Such a method and apparatus could also be applied in the production of solid minerals using a wash or leaching process.
In accordance with the present invention, a method and apparatus is provided for producing fluids from a large area of a subterranean formation through a network of individual horizontal well-bores without:
(i) using complex and expensive drilling, completion and production equipment and techniques to form, operate and maintain such network;
(ii) having to intersect or connect each well-bore with the other well-bores in the network;
(iii) having to equip and operate each well-bore separately; and
(iv) having to construct the entire network immediately before being able to utilize any portion of the network.
The method comprises the steps of: (i) forming a main well-bore having a horizontal section that is located within the formation; (ii) completing and equipping the main well-bore to produce fluids from the formation; (ii) forming one or more additional and separate horizontal well-bores such that the horizontal section of each such additional well-bore is in fluid communication with the horizontal section of the main well-bore without intersecting or connecting with such main well. Only the main well-bore is initially completed and-equipped to produce fluids. However the additional well-bores may be completed to the extent required by government regulation, the art and conditions within the formation. Initially, the additional well-bores are not equipped. The well-bores of these additional or conduit wells act as artificial conduits within the reservoir facilitating the flow of fluids through the reservoir to the well-bore of the main well. By fluids it is meant to include gaseous or liquid substances contained or introduced into a subterranean reservoir or substances contained in the reservoir which can be rendered into a gaseous or liquid phase in-situ within the reservoir, including bitumen, crude oil, heavy crude oil or natural gas.
If the main well-bore fails and can no longer be used to produce substances from the formation, one or more of the additional well-bores may be equipped to produce substances from the formation. In such event the additional well-bore so equipped replaces the main well-bore in function and apparatus It is also possible that in certain applications of the foregoing described process and apparatus, that more than one but not all wells comprising the network, may be completed, equipped and operated in the production of substances from the subterranean formation.
Once the main well-bore has been formed, additional well-bores are formed in sequence. In one embodiment, each additional well-bore is formed such that the horizontal section of such additional well-bore is formed towards or in the direction of the horizontal well-bore of the main well-bore or the horizontal section of an existing additional well-bore which is already in fluid communication with the main well-bore. Prior to and during the forming of an additional well-bore production of fluids from the formation through main well-bore commences and continues. Fluid communication with the main well-bore is determined when drilling fluid being used to form the additional well-bore appears in the fluid being produced from the main well-bore. When this happens loss of circulation in the additional well-bore has or is occurring and further construction of the additional well-bore ceases. To ensure that fluid communication is achieved between the main well-bore and the additional well-bore during the forming of the additional well-bore, it is advisable to produce fluids from the main well-bore for a period of time before commencing to form the additional well-bore.
Where fluid communication between the main well-bore and the additional well-bore, cannot be achieved during the forming of the additional well-bore, then the drilling of the additional well-bore should continue until the horizontal section of the additional well-bore, overlaps or crosses over the horizontal section of the main well-bore or the horizontal section of any existing additional well-bore which is already in fluid communication with the main well-bore. By crosses over, it is meant that the well-bore of the additional well crosses through the vertical plane in which the horizontal section of the main well approximately lies, without intersecting the horizontal section of the main well. By overlaps, it is meant that the well-bore of the additional well lies approximately in the vertical plane in which the horizontal section of the main well approximately lies, without intersecting the horizontal section of the main well.
Where such overlapping or crossing occurs without fluid communication occurring during the forming of the additional well-bore, then communication between the additional well-bore and the main well-bore must be established by the application of means know in the art. This could include the use of techniques such as hydraulic fracturing, perforation or jet washing of a portion of the material comprising the reservoir lying between the horizontal section of the additional well-bore and horizontal section of either the main well-bore or an existing additional well-bore which is already in fluid communication with the main well-bore.
In this manner a large area of the formation may be accessed and produced through a single horizontal well-bore, in communication with a network of horizontal wells, which can be expanded over time or created at once in a shorter period of time. Similarly such a network of communicating horizontal well-bores formed in this manner, may be utilized to inject solvents, heat bearing fluids, reactive fluids or leaching fluids into a formation and produce back such fluids and substances from the formation, through the main well-bore. In this situation, the main well-bore is completed and equipped to both inject and produce fluids from the formation, although in some applications it may not be desirable or necessary to complete and equip such well-bore to inject fluids. The additional well-bores when formed are initially completed and equipped to inject fluids only. Conduct of the fluid injection process can proceed simultaneously through all well-bores or sequentially depending on the nature of the injection fluid and desired result of the fluid injection. The conduct of the injection/production process is continuous until the economic limit for production of fluids from the reservoir is reached. Where the additional well-bores are not initially equipped for the production of substances from the formation, only a small permanent well site may be required at the surface location of each additional well-bore. Where it is not necessary or desirable to access the horizontal section of the additional well-bores subsequent to the forming of the additional well-bores, it may be possible to complete the horizontal section of each additional well-bore and abandon the build and vertical sections of the additional well-bores. This would eliminate the need to construct or maintain a permanent well site for each additional well-bore. Even where a permanent well site is constructed and maintained for the additional well-bores, these wells may not require permanent all weather access roads.
The elimination of permanent well sites and access roads and the reduction of the size of the of the permanent well site is of significant benefit to the environment. For example, in northern muskeg or tundra bearing terrain, the cost and environmental impact of producing heavy crude oil and bitumen through the drilling and operating of a network of wells, can be reduced by drilling the additional well-bores and accessing the wells sites for such well-bores, in the winter over frozen ground. Only the main well-bore, as it is the producing well-bore for the network, requires permanent access and a large permanent well site.
Further environmental benefits can be achieved in terms of the reduction in green house gas emissions. For example in the production of heavy crude oils or bitumen, small amounts of methane and other gases are produced at the well site, in conjunction with the oil being extracted from the reservoir. These gases are frequently vented to the atmosphere, as they do not occur in large enough quantities at any individual well site to physically collect and recover. By producing a heavy oil or bitumen bearing reservoir utilizing a single producing well communicating with a network of wells, the volume of gas production, which is linked to the volume of oil production, can become significant enough to enable the recovery and conservation of the gas. Similarly well site production equipment frequently incorporates heaters and other devices which burn hydrocarbon fuel. The use of a single well to produce a network of communicating well bores, reduces the amount of CO2 being emitted by reducing the number of smaller less efficient well site bumers. Utilizing a single well site with larger more energy efficient production equipment should achieve greater fuel efficiency per barrel of heavy oil, or bitumen produced. Additional green house gas reductions can be achieved, where fluids produced from the reservoir and collected on the surface, such as heavy crude oil or bitumen, must be transported by truck from the point of production, to a remote facility for further processing or sale. Utilizing a single well to produce and collect fluids from a network of communicating wells reduces the distance and trucking time required to gather and transport fluids produced from the network.
Therefore the application of this invention enables a large area of a subterranean formation to be accessed and produced at reduced capital, operating and environmental costs.